The goal of the proposed experiments is to investigate the structural and functional organization of interhemispheric connections of visual areas 17, 18 and 19 in cat cerebral cortex. To achieve this goal, the morphology and synaptology of cells which project axons through the corpus callosum will be determined to ascertain if any of the neurons are non-pyramidal cells which are inhibitory in function. In addition, we will examine the types of synapses which local and long-distance axon collaterals of callosally projecting pyramidal cells form and the nature of their postsynaptic targets. This part of the study will reveal the morphological bases by which callosally projecting neurons in one hemisphere can influence the functions of nearby neurons in the same hemisphere and distant neurons in the contralateral hemisphere. The region of visual space represented in the callosal cell zone and callosal terminal zone of each area will be determined by compiling topographic maps and comparing these maps to the location of the callosal zones defined in the same animal. This part of the study will provide us with insights into the relative contributions played by different cortical areas in one hemisphere in the processing of visual information in the opposite hemisphere. Such insights are important if we are to understand the mechanisms which allow the two hemispheres to operate as an integrated whole.